[DangerZL1]

Originally Posted by Rock-It Man

In general, lowering the upper values is a fuel saving measure. Recommendations went from 40 to 30 and even as low as 20 for some cars. Like all engineering decisions, there are trade-offs. In this case, the trade-off was lubricity during high output driving.

As fo the lower value, there is absolutely no downside to going from 5 to 0, since low viscosity at start-up gets the oil flowing and into gaps more effectively.

But in the end, the most important consideration, for me, is that, given all the variables, which include fits, finishes, and bearing surface materials, the GM engineers know what's best, and not you and me.

I too trust what the GM recommended oil is and see no reason to change in a stock car driven on the street.